Die paddle clamping method for wire bond enhancement

ABSTRACT

A leadframe configuration for a semiconductor device has a die attach paddle with paddle support bars. In addition, clamp tabs extend outwardly from lesser supported locations of the paddle to underlie a conventional lead clamp. The clamp tabs are formed as an integral part of the paddle. Normal clamping during die attach and wire bonding operations prevents paddle movement and enhances integrity of the die bond and wire bonds.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 09/210,013,filed Dec. 11, 1998, now U.S. Pat. No. 6,162,662, issued Dec. 19, 2000,which is a divisional of application Ser. No. 09/028,133, filed Feb. 23,1998, now U.S. Pat. No. 6,121,674, issued Sep. 19, 2000.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to a semiconductor device assemblyincluding a semiconductor die and leadframe. More particularly, theinvention pertains to a leadframe with a mounting paddle to which asemiconductor die is bonded and with a plurality of leads of theleadframe connected to the bond pads on the die by wire bonding.

2. State of the Art

In the manufacture of semiconductor device assemblies, a singlesemiconductor die is most commonly incorporated into each sealedpackage. Many different package styles are used, including dual inlinepackages (DIP), zig-zag inline packages (ZIP), small outline J-bends(SOJ), thin small outline packages (TSOP), plastic leaded chip carriers(PLCC), small outline integrated circuits (SOIC), plastic quad flatpacks (PQFP), and interdigitated leadframe (IDF). Some semiconductordevice assemblies are connected to a substrate, such as a circuit board,prior to encapsulation.

The assembly of a semiconductor device and a leadframe and dieordinarily includes bonding of the die to a paddle of the leadframe, andwire bonding bond pads on the die to inner leads, i.e. lead fingers, ofthe leadframe. The inner leads, semiconductor die, and bond wires arethen encapsulated, and extraneous parts of the leadframe excised.

In drawing FIG. 1, an exemplary PRIOR ART leadframe strip 10 is shown.The leadframe strip 10 comprises a thin metal foil. The leadframe strip10 is configured for the mounting of a plurality of semiconductor dice,one on each die mount paddle 12. The leadframe strip 10 also includesparallel spaced side rails 14, 16 formed with a pattern of registryholes 18 for handling by automatic machinery. In addition, the leadframestrip 10 includes an arrangement of inner leads 20 configured forattachment to the bond pads of a semiconductor die during a wire bondingstep. Outer leads 22 will become the external leads of the completedsemiconductor device package for connection to, e.g., a circuit board.The leads 20, 22 are connected to the side rails 14, 16 by dam bars 24,and supported thereby. As shown, each of the die mount paddles 12 isconnected to each of the side rails 14, 16 by a paddle support bar 26,28, respectively, extending transversely with respect to the centerline30 of the leadframe strip 10.

In an alternative arrangement, not shown, the paddle support bars 26, 28extend parallel to centerline 30 from the die mount paddles 12 to dambars 24 for support of the paddles.

In forming a semiconductor device package, semiconductor dice aretypically bonded to the paddles of the leadframe strip with an adhesivepolymer, such as epoxy or a thermoplastic, with soft solder, or with agold-silicon eutectic layer. Generally, each paddle is slightly largerthan the attached semiconductor die. The conductive bond pads of thesemiconductor die are then wire bonded to the inner leads surroundingthe semiconductor die, generally by the use of the well-knownthermocompression bonding method, but sometimes by thermosonic orultrasonic bonding methods.

During semiconductor die attach and wire bonding, the inner leads aretypically clamped against a lower heater block or other flat member. Thebonding tool itself is configured to compress the wire against thesurface to which the wire is being bonded, i.e. bond pad or inner lead.Examples of such are found in U.S. Pat. No. 4,600,138 of Hill, U.S. Pat.No. 4,030,657 of Scheffer, U.S. Pat. No. 4,603,803 of Chan et al., U.S.Pat. No. 4,778,097 of Hauser, U.S. Pat. No. 5,148,959 of Cain et al.,U.S. Pat. No. 5,217,154 of Elwood et al., U.S. Pat. No. 5,421,503 ofPerlberg et al., and U.S. Pat. No. 5,445,306 of Huddleston. generallybeen found, however, that auxiliary clamping apparatus may improve thequality of “second bonding”, i.e., bonding of the wire to the innerleads.

Each inner lead being wire bonded may be clamped while being wire bondedonly, or all leads may be simultaneously clamped.

Commercial wire bonding machines typically have an upper clamp memberwhich includes a window for access to the semiconductor die, die paddleand inner end portions of the inner leads. The “frame” of the windowacts as a narrow clamp which simultaneously holds down the inner leadssurrounding the semiconductor die against the heater block.Alternatively, clamps are inserted through a window to hold the innerleads against the heater block. These “window” types of clampingarrangements are exemplified in U.S. Pat. No. 3,685,137 of Gardiner,U.S. Pat. No. 5,035,034 of Cotney, U.S. Pat. No. 5,322,207 of Fogal etal., U.S. Pat. No. 5,372,972 of Hayashi et al., U.S. Pat. No. 4,765,531,5,238,174 and 5,307,978 of Ricketson et al., U.S. Pat. No. 5,082,165 ofIshizuka, and U.S. Pat. No. 5,264,002 of Egashira et al.

Various other types of prior art clamping apparatus and methods ofclamping an inner lead or bond pad against a flat lower member areillustrated in U.S. Pat. No. 4,361,261 of Elles et al., U.S. Pat. No.4,434,347 of Kurtz et al., U.S. Pat. No. 4,978,835 of Luijtjes et al.,U.S. Pat. No. 5,193,733 of You, U.S. Pat. No. 5,197,652 of Yamazaki,U.S. Pat. No. 4,821,945 of Chase et al., and U.S. Pat. 5,647,528 of Ballet al.

U.S. Pat. No. 3,566,207 of Adams shows a leadframe in which the paddlesupport bars are clamped by “point” clamps.

A major source of package rejection is wire bond failure. Such failurehas been attributed to overheating, underheating, chemicalcontamination, surface roughness, surface voids, oxide formation,presence of moisture, inadequate lead clamping, and other suspectedcauses.

While a wire bond “no-stick” may sometimes be detected and reworked onthe spot, wire bond defects often do not become apparent untilsubsequent testing, or after the device has been encapsulated and/or hasbeen in use. At this stage, the unit cost of the device itself ismaximal. In addition, repair of a defective device may not be feasible.

On occasion, the die-to-paddle bond fails and may result in, e.g.,shorting within the packaged device, wire bond breakage, loss of heatdissipation capability, and/or incomplete sealing of the package.

Even a relatively low frequency of defects in the wire bonds and indie-to-paddle bonds is extremely costly to the semiconductor industry.

It is therefore an object of the invention to provide a semiconductordevice wherein the frequency of wire bond failures and die-to-paddlebond failures is reduced, the frequency of required wire bond rework isreduced, and the manufacturing cost is reduced.

BRIEF SUMMARY OF THE INVENTION

It has been generally assumed in the industry that the die mount paddledoes not move during down-bonding of the semiconductor die, or duringsubsequent wire bonding. However, it has been discovered thatsignificant movement sometimes may exist, and this movement contributesto poor semiconductor die-to-paddle bonding and can be a major cause ofthe observed failure, i.e., immediate “no-stick” or subsequent debondingof the wire bonds from the bond pads of the semiconductor die and/orfrom the metal inner leads.

In accordance with the invention, the pattern of paddle and leads on theleadframe is configured to provide a paddle with clampable tabsextending therefrom. The tabs extend outwardly from areas of the paddlewhich are otherwise largely unsupported or farthest from the paddlesupport bars. These tabs may be formed on the sides of the paddle alongwhich there are few, if any, bond pads. Alternatively, the tabs may beon the same sides as the paddle support bars, particularly when thepaddle support bars on the sides have few, if any, bond pads. Typically,the tabs are positioned on the long dimensions of the paddle. When theleadframe is clamped for die attach and wire bonding, a clamp membersuch as a circumscribing “window frame” simultaneously clamps the innerleads, paddle support bars and paddle tabs against a lower clamp memberwhich may be a heater block. The paddle is thus more extensivelysupported and is much more resistant to flexing, bending, and liftingaway from the lower clamp member during the bonding operations.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The invention is illustrated in the following figures, wherein theelements are not necessarily shown to scale:

FIG. 1 is a plan view of a prior art semiconductor leadframe strip;

FIG. 2 is a plan view of a wire-bonded semiconductor device having aleadframe of the invention;

FIG. 3 is a cross-sectional side view of a portion of a leadframe stripof the invention and a die bonded thereto, as taken along line 3—3 ofFIG. 2;

FIG. 4 is a cross-sectional side view of a portion of another embodimentof a leadframe strip of the invention and a die bonded thereto, as takenalong line 3—3 of FIG. 2; and

FIG. 5 is a plan view of a wire-bonded semiconductor device havinganother embodiment of a leadframe of the invention.

DETAILED DESCRIPTION OF THE INVENTION

In the following discussion, the terms “upper” and “lower” areunderstood to include the inverse when referring to clamp members orleadframe levels of a bilevel leadframe.

As depicted in drawing FIGS. 2 and 3, a portion of an uncompletedexemplary semiconductor device 40 includes a semiconductor die 42 and ametal leadframe strip 44 to which the semiconductor die is attached. Thefinal package outline 74 is shown with centerline 45. The leadframestrip 44 includes inner leads 46, outer leads 48, and spacedapart siderails 50 and 52 for each of a plurality of leadframe panels 54. Theinner leads 46 and outer leads 48 are supported from the side rails 50,52 by dam bars 76. The outer leads 48 for the leadframe are only shownin part, but generally extend to a crossbar, not shown, or to thecorresponding outer leads of the adjacent leadframe panels 54 ofleadframe strip 44.

The leadframe strip 44 also includes a die mount paddle 60 which isconfigured for the mounting of the back side 62 of semiconductor die 42thereon, using an adhesive layer 104 such as polyimide, epoxy, polymerictape, etc. The adhesive layer 104 may be electrically nonconductive orconductive, depending upon the particular use for which the device isdesigned. The die mount paddle 60 is connected at each end 56, 58 to oneof the leadframe rails 50, 52 by paddle support bars 78 and 80, and issupported thereby.

The semiconductor die 42 is illustrated as having an active surface 64with a generally rectangular shape, although the semiconductor die maybe of any shape. Bond pads 66 are arrayed adjacent the semiconductor dieends (edges) 68, 70 for conductive attachment to the inner leads 46 withthin wires 72. The wire bonding process may be one of thermocompression,ultrasonics or thermosonics, for example.

In accordance with the invention, the die mount paddle 60 is formed withclamping tabs 90 on each non-supported side 82, 84, i.e., the sides nothaving a paddle support bar 78, 80. Each clamping tab 90 extendsoutwardly to underlie the upper clamp member 86 and may be clampedthereby to a lower clamp member, not shown, which underlies a majorportion of the leadframe panel 54. The clamping tabs 90 are shown withouter ends 88 not connected to inner leads 46, side rails 50, 52, orother parts of the leadframe panel 54. Thus, the presence of theclamping tabs 90 does not affect the choice of conductive ornonconductive adhesive layer 104. The clamping tabs 90 are configured tobe totally encapsulated in the completed packaged device 40.

Drawing FIG. 2 shows two clamping tabs 90 on each side 82, 84 of the diemount paddle 60, the clamping tabs 90 extending outwardly and convergingtoward each other. The clamping surface 102 of the upper clamp member 86intersects and exerts clamping force on the tab clamping areas 106 ofthe clamping tabs 90. The clamping tabs 90 may take any reasonable shapewhich will make the die mount paddle 60 more rigid but not result inshorting to leads or wires, and will not hinder polymer passage duringencapsulation. Thus, the spacing 108 between the clamping tabs 90 andadjacent inner leads 46 and the space 110 between the two clamping tabs90 permit adequate flow of polymer. The clamping tabs are shown ashaving a width comparable to the outer leads 48.

Preferably, the clamping tabs 90 are positioned so that there is no needfor bond wires 72 to pass over the tabs.

As shown in the cross-sectional view of drawing FIG. 3, the inner leads46 and die mount paddle 60 may be coplanar, and the upper clamp member86 has a clamping surface 102 which surrounds wire-bonding access window87 and compresses the inner leads 46, die mount paddle 60 and, clampingtabs 90, as well as the paddle support bars 78, 80 (not visible) againstthe flat surface 98 of the lower clamp member 96, e.g., heater block.

An alternative configuration is shown in drawing FIG. 4, in which thedie mount paddle 60 is depressed to a lower level 92 below an upperlevel 94 of the inner leads 46. The paddle support bars (see bar 78) andthe clamping tabs 90 are bent upwardly from the die 42 so that outerportions thereof underlie the clamping surface 102 of the upper clampmember 86 for firm clamping to the lower clamp member 96, e.g., heaterblock. While a packaged semiconductor device may be made with thisalternate configuration, the coplanar configuration of drawing FIG. 3 isgenerally preferred for ease of manufacture.

Drawing FIG. 5 depicts a variation, alternative embodiment, of theinvention in which the clamping tabs 90 also act as paddle support bars.

As shown in drawing FIG. 5, a portion of an uncompleted exemplarysemiconductor device 40 includes a semiconductor die 42 and a metalleadframe strip 44 to which the die 42 is attached. The final packageoutline 74 is shown with centerline 45. The leadframe strip 44 includesinner leads 46, outer leads 48, and side rails 50 and 52. The innerleads 46 and outer leads 48 are supported from the side rails 50, 52 bydam bars 76.

The leadframe strip 44 also includes a die mount paddle 60 which isconfigured for the mounting of the semiconductor die 42 thereon, aspreviously described.

The semiconductor die 42 is illustrated as having an active surface 64with a generally rectangular shape. Bond pads 66 are arrayed adjacentthe die ends (edges) 68, 70 for conductive attachment to the inner leads46 with thin wires 72. The wire bonding process may be one ofthermocompression, ultrasonics or thermosonics, for example.

In accordance with this embodiment of the invention, the die mountpaddle 60 is formed with clamping tabs 90 on each of the sides 114, 116having no (or few) bond pads 66. In contrast to the version shown indrawing FIGS. 2-4, the ends 56, 58 of the die mount paddle 60 are notconnected to the side rails 50, 52 by support bars. Each clamping tab 90is integral with the die mount paddle 60 over a major portion of theside 114 or 116. Each clamping tab 90 extends outwardly to underlie theupper clamp member 86 in tab clamping area 106 and may be clampedthereby to a lower clamp member, not shown, which underlies a majorportion of the leadframe strip 44. The clamping tabs 90 are shown withconstricted outer ends 88 connected to dam bars 76 for supporting thedie mount paddle 60 during die bond and wire bonding operations. Eachclamping tab 90 is shown with apertures 112 therethrough whereby theflow of liquified polymer during device encapsulation is notdeleteriously impeded. The clamping tabs 90 are configured to be totallyencapsulated in the completed packaged device 40.

The clamping tabs 90 may take any reasonable shape which will not resultin shorting to leads or wires, and will not hinder polymer movementduring encapsulation. Preferably, the clamping tabs 90 are positioned sothat there is no need for bond wires 72 to pass over the tabs.

Following encapsulation, the tab ends 88 are severed, and the dam bars76 removed to singulate the leads.

If desired, the die mount paddle 60 may be formed of a materialdifferent from the inner leads 46 and outer leads 48. In the currentstate of the art, however, additional cost would be incurred.

A major advantage of the inclusion of clamping tabs 90 in the die mountpaddle 60 is the prevention of paddle movement during die bonding andthe subsequent wire bonding operations. The reduced movement permitsmore secure bonding of the semiconductor die 42 to the die mount paddle60. In addition, the first wire bond, i.e., to the bond pad 66, as wellas the second wire bond, i.e., to an inner lead 46, are stronger. As aresult, the device failure rate may be significantly reduced.

An additional advantage of the invention is the enhanced heat spread anddissipation through the clamping tabs.

It is apparent to those skilled in the art that various changes andmodifications may be made to the leadframe configurations of theinvention, devices formed therefrom and methods of making and practicingthe invention as disclosed herein without departing from the spirit andscope of the invention as defined in the following claims.

What is claimed is:
 1. A method of assembling a semiconductor deviceassembly using a clamp including an upper clamp member and a lower clampmember of a wire bonding apparatus, said method comprising: forming astrip of lead frames, said strip having opposed rails, having dam barsbetween said opposed rails, having inner leads, having outer leads,having a die mount paddle and having at least one integral clamping tab,said at least one integral clamping tab extending outwardly for contactby said upper clamp member; attaching a semiconductor device to said diemount paddle, said semiconductor device having an active surface havinga plurality of bond pads located thereon; aligning said strip of leadframes on said lower clamp member of said wire bonding apparatus havingsaid upper clamp member overlying portions of said inner leads andportions of said outer leads of said at least one clamping tab; andattaching a plurality of bond wires to said plurality of bond pads onsaid active surface of said semiconductor device and portions of saidinner leads.
 2. The method of claim 1, further comprising: forming saiddie mount paddle having the upper surface thereof at a level below anupper level of said inner leads; and deforming said at least oneclamping tab to clamp portions thereof.
 3. The method of claim 1,further comprising: removing said strip of lead frames and saidsemiconductor device from said clamp; and encapsulating a portion ofsaid strip of lead frames, said semiconductor die, and said plurality ofbond wires extending between said strip of lead frames and saidsemiconductor device in a material.